FIELD OF THE INVENTION
The invention relates to a method for monitoring the operation of a sensor in an internal combustion engine and an electronic controller monitoring the operation of a sensor.
The growing dependency on fundamental functions in motor vehicles--such as ignition, injection, and knock control--by electronic control systems is placing extremely stringent requirements on their reliability. Furthermore, reliable electronic control systems demand reversionary running programs for fault situations. Self-diagnosis is thus one of the basic functions in modern microprocessor-controlled systems. The objects of self-diagnosis in such control systems are to identify faults and to evaluate them diagnostically, to protect endangered components by suitable reversionary running programs, to provide any substitute parameters required for reversionary running, and to transmit a fault message to the driver.
Under normal operation, sensors derive measurement values from the sensor signals in an evaluation circuit. For example, sensors can derive measurement values of the voltage or current levels. The current levels are proportional to the sensor signal. The evaluation circuit checks these measured values for plausibility by comparing them with plausibility limit values. Depending on the nature of the sensor, a malfunction of the sensor is diagnosed if the plausibility limit value is infringed in either direction over a number of measurement cycles.
For knock control, such a method is known from Published, Non-Prosecuted Patent Application DE 41 26 961 A1, corresponding to U.S. Pat. No. 5,121,729. In order to suppress knocking in an internal combustion engine, a measured value is produced in an evaluation circuit from the sensor signals from a knock sensor, cyclically synchronized with time intervals. The time intervals are defined by the engine cycles of the internal combustion engine.
This measured value is then compared with a fixed plausibility limit value. If the measured value remains below the plausibility limit value throughout a predetermined number of engine cycles in this case, a malfunction of the knock sensor is diagnosed and the ignition is delayed in order to suppress the knocking.
However, in methods such as this, fault identification is feasible only if the measured value in the event of a fault is outside a plausibility range that is governed by the correctly operating sensor.